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Viruses: Glossary


a chemical substance that kills or inhibits the growth of bacteria
a protein molecule in the blood serum or other body fluids that destroys or neutralizes bacteria, viruses, or other harmful toxins
a foreign substance that stimulates the immune system to produce antibodies. Antigens can be substances like bacteria, viruses, or even pollen that invade the body. There's a different antigen for every cold you've ever had


single-celled organisms. Bacteria are bigger than viruses, but still too small for you to see. There are thousands of types of bacteria, and they live everywhere. Bacteria are much more complex than viruses. Bacteria have the tools to reproduce themselves, by themselves. They are filled with fluid, and may have threadlike structures, like a tail, to move themselves
bone marrow
soft tissue located in the cavities of the bones where blood cells are formed, including erythrocytes, leukocytes, and platelets


an organism that carries a virus either in the form of an infection or while it is in incubation
a small, enclosed unit containing the DNA, proteins, and chemicals needed for life functions. The fundamental unit of life
any infectious disease that can be passed with just casual contact from from one person to another


electron microscope
an instrument that allows us to look at very small items too small to see with an optical microscope. It uses a focused beam of electrons to enlarge the image of an object on a screen or photographic plate


genetic instructions
the directions that tell a living cell how all the molecules in its DNA are organized
genetic material
any material of plant, animal, microbial or other origin containing all the information necessary to make a new copy of the organism


a cell or organism in which a parasite or virus is growing


immune system
different types of cells, tissues and enzymes all cooperating with each other that identify and eliminate threatening foreign elements from our bodies. Each part of the immune system network has it's own specialized task. The immune system can remember its response later if the foreign substance invades the body again
affected with a disease-causing organism
infectious disease
condition in which virulent organisms are able to multiply within the body and cause a response from the host's immune system


a clear fluid that travels through the lymphatic system and carries cells that help fight infections and other diseases
lymph nodes
rounded masses of lymphatic tissue. Lymph nodes filter lymph, and they store white blood cells. They are located along lymphatic vessels
a type of white blood cell involved in the body's immune defense system. There are a few different kinds of lymphocytes: the natural killer cells (NK cells), the T cells, and B cells
lymph vessels
thin tubes that carry lymph and white blood cells through the lymphatic system. They branch, like blood vessels, into all parts of the body


also known as a microorganism, is an organism that is microscopic (too small to be visible to the naked eye). We also call them "germs."
an instrument for viewing objects that are too small to be seen by the unaided eye. The word "microscopic" means very small, and it comes from the Greek word: micron, which means "small" and scopos, which means "aim."
so small as to be visible only with a microscope


a family of one-celled organisms that are the simplest form of animal life. AIDS, Toxoplasmosis, Pneumocystis carinii, Giardia, and Cryptosporidium belii are all harmful protozoa


the biological process by which new individual organisms are made


an organ on the left side of the abdomen, near the stomach. It produces some white blood cells, filters the blood, stores blood cells, and destroys old blood cells


an organ in the chest behind the breastbone. Lymphocytes grow and multiply in the thymus


helps your immune system to fight a certain illness. A vaccine is usually made of the same cells that could make you sick, but they are weak or inactive. Sometimes a vaccine is made of cells that are very close, but not exactly the same, to the cells that would make you sick
the study of viruses and viral diseases. A virologist is a scientist who studies virology
a submicroscopic particle that can infect the cells of a biological organism. Virus comes from the Latin word for "poison."


white blood cells
made by bone marrow and help the body fight infection and other diseases. There are different types of white blood cells, each with a different job
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